1. Field of the Invention
The disclosure relates to a heat exchanging device.
2. Description of the Related Art
Japanese Patent Application Laid-open No. 2007-085457 discloses a heat exchanging device mounted on a vehicle. The heat exchanging device which performs heat exchange between operating oil (engine oil) used in an engine and operating oil (transmission oil) used in an automatic transmission is configured to heat the transmission oil by the engine oil at the time of cold start of the engine.
In a vehicle on which an automatic transmission is mounted, a fluid transmitting device (torque converter) is provided between an engine and the automatic transmission. The fluid transmitting device filled with operating oil is provided with a lock-up mechanism. The fluid transmitting device engages or disengages the lock-up mechanism by hydraulic pressure supplied from a hydraulic circuit. The hydraulic circuit is configured to supply the automatic transmission being a lubricating unit with oil together with the fluid transmitting device and circulate the oil. That is, the same oil is used in the fluid transmitting device and the automatic transmission, so that a state of the fluid transmitting device relates to temperature change of the transmission oil. However, the state of the fluid transmitting device and the lock-up mechanism is not taken into consideration in the heat exchanging device disclosed in Japanese Patent Application Laid-open No. 2007-085457.
Therefore, the inventors of the present invention execute an evaluation test for clarifying the relationship between the temperature change of the transmission oil and the state of the fluid transmitting device after cold start of the engine. An evaluation result is illustrated in FIG. 12. FIG. 12 is a time chart illustrating the evaluation result when the vehicle travels at an arbitrary vehicle speed after the cold start of the engine. Meanwhile, in the evaluation test illustrated in FIG. 12, control to prohibit the engagement of the lock-up mechanism when a temperature of the transmission oil is lower than a predetermined temperature after the cold start of the engine and allow the engagement of the lock-up mechanism when the temperature of the transmission oil is not lower than a predetermined temperature is executed.
In an example illustrated in FIG. 12, immediately after the cold start of the engine, the temperature of the transmission oil is lower than a predetermined temperature and it is prohibited to engage the lock-up mechanism, so that the lock-up mechanism is disengaged before time point t1 (L/U: OFF). Thereafter, the temperature of the transmission oil becomes not lower than the above-described predetermined temperature at time point t1, and according to this, the lock-up mechanism is engaged (L/U: ON). The temperature of the transmission oil at time point t1 at which the engagement of the lock-up mechanism is started is set to an L/U starting temperature. In a state in which the lock-up mechanism is disengaged before time point t1, a heat exchanging amount of the transmission oil takes a negative value as a result of the heat exchange between the engine oil and the transmission oil. This indicates that heat transfers from the transmission oil to the engine oil. When the heat exchanging amount takes a positive value, the transmission oil temperature rises, and when the heat exchanging amount takes the negative value, the transmission oil temperature falls. Therefore, before time point t1, a transmission oil temperature TOUT after passing through the heat exchanger is such that the temperature with the heat exchange is lower than the temperature without the heat exchange.
The inventors of the present invention learn that the transmission oil temperature is higher than an engine oil temperature and the heat transfers from the automatic transmission to the engine during a warm-up of the automatic transmission (initial stage of warm-up) from the evaluation result illustrated in FIG. 12. It is considered that a fact that a pump impeller and a turbine runner rotate relative to each other in the fluid transmitting device and the operating oil is shaken to generate the heat in the fluid transmitting device due to the disengagement of the lock-up mechanism at the initial stage of the warm-up has a relationship with a rise in the transmission oil temperature.
When the heat transfers from the automatic transmission to the engine at the time of the warm-up of the automatic transmission, the rise in the temperature of the transmission oil delays and fuel consumption is deteriorated as indicated in the evaluation result illustrated in FIG. 12.
There is a need for a heat exchanging device mounted on the vehicle provided with the engine, the fluid transmitting device, the lock-up mechanism, and the automatic transmission, the heat exchanging device which promotes the rise in the temperature of the transmission oil at the time of the warm-up of the automatic transmission to improve the fuel consumption.